This invention relates generally to pressure operated relief valves and more particularly concerns a novel two-stage pilot valve having substantially larger capacity at predetermined pressures. Specifically, the valve disclosed provides improved main valve operation through control of pressure dynamics of the combination pilot, main valve and associated pressure conduit or vessel. An improved method of calibrating and testing pressure sensitive elements is also provided.
Prior art relief and/or valve combinations are disclosed in U.S. Pat. Nos. 3,595,263, 3,664,362, 3,512,560, and 3,568,706. However, although the operation provided by these combinations of main and pilot valves is acceptable, adequate control of the dynamic relationships between the pilot valve, main valve, and pressure vessel or conduit is difficult to achieve. In addition, the prior art valves, in many cases, when tested on site, provide a method of testing only a pilot valve set point. Therefore, reset or blowdown pressure setting of the pilot valve and the main valve operation remain untested. The pilot valve disclosed herein provides for on site testing of pilot set point, blowdown, or reset pressure, and main valve, or alternately the pilot valve alone, through the use of small quantities of an auxiliary test gas.
Therefore, it is an object of the invention to provide an improved two-stage pilot valve for operation of a larger capacity pressure relief valve wherein test operation of the first stage pilot is possible without operation of the main valve.
It is an object of the invention to provide a pressure relief valve of substantial capacity having improved control of the product flow and pressure dynamics associated with the pilot valve, main relief valve, and pressure vessels or conduits requiring pressure relief.
It is a further object of the invention to provide an improved two-stage pressure sensitive pilot valve, wherein flow of the product, exerting the sensed pressure, through each stage of the valve occurs only during relief or reset operation of the pilot.
It is still a further object of the invention to provide a two-stage pressure operated pilot valve for operating main relief valves of substantially larger capacity where greatly reduced flow through the pilot can be highly filtered providing increased reliability through a reduction in contamination.